Helminths – FRCPath Part 2 Short Notes
1. Trematodes (Flukes)
Schistosoma spp.
- Epidemiology/Geography:
- S. haematobium → Africa, Middle East.
- S. mansoni → Africa, Middle East, South America, Caribbean.
- S. japonicum → China, Philippines, SE Asia.
- Transmission: Skin penetration by cercariae from freshwater snails.
- Clinical:
- S. haematobium → urinary schistosomiasis, ↑ bladder carcinoma risk.
- S. mansoni → intestinal + hepatosplenic disease.
- S. japonicum → more severe hepatosplenic disease.
- Diagnostics: Eggs in stool/urine (terminal vs lateral spines), serology, antigen detection (CCA).
- Treatment: Praziquantel (40 mg/kg).
- Public health: WHO mass drug administration (MDA).

Clonorchis sinensis / Opisthorchis spp.
- Geography: China, Korea, Vietnam, Thailand, Laos, Cambodia.
- Transmission: Ingestion of metacercariae in raw freshwater fish.
- Clinical: Biliary obstruction, cholangitis, cholangiocarcinoma risk.
- Diagnostics: Small operculated eggs in stool.
- Treatment: Praziquantel.



Small operculated egg
Fasciola hepatica
- Epidemiology: Sheep-raising areas worldwide; watercress ingestion.
- Transmission: Ingestion of metacercariae on aquatic plants.
- Clinical: Acute (fever, RUQ pain, eosinophilia); chronic (biliary obstruction).
- Diagnostics: Large operculated eggs in stool, serology.
- Treatment: Triclabendazole (not praziquantel).


Paragonimus westermani
- Epidemiology: Asia; raw/undercooked freshwater crab/crayfish.
- Clinical: Pulmonary infection (cough, haemoptysis, TB mimic); ectopic CNS disease.
- Diagnostics: Operculated eggs in sputum/stool.
- Treatment: Praziquantel.

2. Cestodes (Tapeworms)
Taenia saginata / Taenia solium
- Epidemiology: Worldwide, esp. where beef/pork undercooked.
- Transmission: Ingestion of cysticerci in meat.
- Clinical: Intestinal taeniasis; T. solium → cysticercosis (CNS seizures).
- Diagnostics: Eggs (radial striations), proglottids in stool; neuroimaging + serology for cysticercosis.
- Treatment:
- Praziquantel/niclosamide (intestinal);
- albendazole + steroids (neurocysticercosis).
Differences: saginata is cattle, tapeworms longer (up to 10m), unarmed, more uterine branches, intestinal only.
Echinococcus granulosus (dog) / multilocularis (fox)
- Epidemiology: Sheep-raising regions (Mediterranean, Middle East, South America, China).
- Transmission: Ingestion of eggs from dog faeces.
- Clinical: Hydatid cysts (liver, lung); rupture → anaphylaxis; E. multilocularis → invasive hepatic disease.
- Diagnostics: Imaging (US/CT), serology.
- Treatment: Albendazole ± PAIR (puncture-aspiration-injection-reaspiration) or surgery.

Diphyllobothrium latum
- Epidemiology: N. Europe, Japan; raw freshwater fish.
- Clinical: Intestinal tapeworm; B12 deficiency → megaloblastic anaemia.
- Diagnostics: Operculated eggs in stool.
- Treatment: Praziquantel.

Hymenolepis nana
- Epidemiology: Worldwide, esp. children.
- Transmission: Ingestion of eggs; autoinfection possible.
- Clinical: Diarrhoea, abdominal pain.
- Diagnostics: Eggs in stool (polar filaments).
- Treatment: Praziquantel.
3. Nematodes (Roundworms)
Ascaris lumbricoides
- Epidemiology: Most common helminth worldwide.
- Transmission: Ingestion of embryonated eggs in contaminated food/soil.
- Clinical: Loeffler’s pneumonitis (larval migration), intestinal obstruction, biliary colic.
- Diagnostics: Large mammillated eggs in stool.
- Treatment: Albendazole/mebendazole.

Trichuris trichiura (Whipworm)
- Transmission: Ingestion of eggs.
- Clinical: Dysentery, rectal prolapse in heavy infections.
- Diagnostics: Barrel-shaped eggs with bipolar plugs.
- Treatment: Albendazole/mebendazole.

Enterobius vermicularis (Pinworm)
- Epidemiology: Common in children.
- Transmission: Ingestion of eggs (perianal → hand → mouth) > autoinfection
- Clinical: Perianal itch (worse at night).
- Diagnostics: “Scotch tape test.”
- Treatment: Mebendazole; treat household contacts.

Strongyloides stercoralis
- Transmission: Skin penetration by larvae.
- Clinical: Asymptomatic or mild diarrhoea; hyperinfection in immunocompromised (esp. steroids, HTLV-1), associated with Gram negative sepsis
- Diagnostics: Rhabditiform larvae in stool, serology, PCR.
- Treatment: Ivermectin (not albendazole).

Hookworms (Ancylostoma duodenale, Necator americanus)
- Transmission: Skin penetration by larvae.
- Clinical: Iron deficiency anaemia, malnutrition.
- Diagnostics: Thin-shelled eggs in stool.
- Treatment: Albendazole/mebendazole.

Trichinella spiralis
- Transmission: Ingestion of encysted larvae in undercooked pork/wild game.
- Clinical: Myositis, fever, eosinophilia, periorbital oedema.
- Diagnostics: Muscle biopsy, serology.
- Treatment: Albendazole/mebendazole + steroids if severe.
Dracunculus medinensis (Guinea Worm)
- isolated cases in Chad/Ethiopia
- Transmission: Drinking water with copepods carrying larvae.
- Clinical: Painful skin ulcer with emerging worm.
- Diagnostics: Clinical.
- Treatment: No drug; slow extraction of worm. WHO eradication programme.
Toxocara canis/cati
- Transmission: Ingestion of dog/cat roundworm eggs.
- Clinical: Visceral larva migrans, ocular larva migrans.
- Diagnostics: Serology (ELISA), eosinophilia.
- Treatment: Albendazole ± steroids.
Filarial worms
- Wuchereria bancrofti / Brugia malayi
- Geography: Africa, Asia, Pacific, India.
- Transmission: Mosquito bite.
- Clinical: Lymphatic filariasis → elephantiasis.
- Diagnosis: Peripheral films
- Treatment: DEC + albendazole.
- Loa loa
- Geography: West and Central Africa (rainforest belt).
- Transmission: Chrysops fly (day-biting).
- Clinical: Calabar swellings, migrating eye worm.
- Treatment: DEC (caution with high microfilarial loads).
- Onchocerca volvulus
- Geography: Sub-Saharan Africa, Yemen, Central/South America (riverine areas).
- Transmission: Blackfly (fastflowing riverine areas).
- Clinical: River blindness, dermatitis, hanging groin.
- Diagnostics: Skin snip microfilariae.
- Treatment: Ivermectin (DEC contraindicated due to Mazzotti reaction).
4. Tissue Nematodes (Zoonotic)
Anisakis spp.
- Epidemiology: Japan, raw/undercooked marine fish.
- Clinical: Acute abdominal pain (gastric anisakiasis).
- Diagnostics: Endoscopy (larva).
- Treatment: Endoscopic removal.
Capillaria philippinensis
- Transmission: Ingestion of raw freshwater fish.
- Epidmiology: Phillipines, Thailand
- Clinical: Malabsorption, chronic diarrhoea, wasting.
- Treatment: Albendazole.
🔑 Extra Exam Pearls
- Eosinophilia → classic for tissue-migrating helminths (schistosomes, strongyloides, filariae, trichinella, toxocara).
- Cancer links → S. haematobium (bladder), Clonorchis/Opisthorchis (cholangiocarcinoma).
- Treatment pitfalls →
- Fasciola → triclabendazole (not praziquantel).
- Strongyloides → ivermectin (not albendazole).
- Onchocerca → ivermectin (not DEC).
- Public health →
- Schisto MDA with praziquantel.
- Filariasis elimination with DEC + albendazole.
- Guinea worm near-eradication.
- Diagnostics → stool/urine microscopy, serology, antigen tests, PCR, imaging (hydatid, neurocysticercosis).
- Other → Echinococcus cysts (risk of anaphylaxis), Strongyloides hyperinfection in immunosuppressed.
